Continued Advances in the Research of a Cu-Ni/Sn High Temperature Pb-Free Composite Solder Paste

Abstract: A promising Cu-Ni/Sn lead-free alternative to high-Pb solder, consisting of a composite mixture of SN100C (Sn- 0.7Cu-0.05Ni) commercial solder powder and Ames Lab’s gas atomized Cu-10Ni, wt.%, powder is being completed to improve the reliability and survivability of PCB and SMT solder joints operating under extreme temperatures (Tm~525°C). The designed paste is predicted to be nearly 4,000 times less expensive than the currently available HTLF (high-temperature lead-free) solder Au-20Sn, wt.%, and able to withstand higher temperatures while still maintaining a standard commercial processing temperature of around 250°C. The paste performs using liquid-phase diffusion bonding (LPDB) of the high-melting Cu-10Ni powders into the low-melting SN100C to form the roomtemperature stable intermetallic compound (IMC) (Cu,Ni)6Sn5. The nickel addition to this high-temperature phase increases joint ductility by suppressing the brittling transformation of the IMC into the low-temperature phase. New research explores limits of the paste’s reflow profile, decreasing void formation in the joints, and high temperature mechanical strength measurements. Results suggest that this composite paste could be an excellent “drop-in” replacement for the Pb-based high-temperature solders soon to be eliminated by RoHS. Foundation and Nihon-Superior, Inc. Ltd., through Ames Lab (DE-AC02- 07CH11358) is gratefully acknowledged.